1. Field of the Invention
The present invention relates to a name server for processing a reverse look-up request, a name server for processing a normal look-up request, a network system, a reverse look-up request processing method, a normal look-up request processing method, and a communication control method.
2. Description of the Related Art
In recent years, in conjunction with the spread of the constant access to the Internet even at general homes, the privacy issue is attracting attentions. For example, increasingly many people are concerned about the leakage of the privacy of the communication device (communication node) or the user who is using it by using the IP address as a key.
In particular, in the IPv6 environment in general, a specific prefix is assigned to the upper 64 bits from the ISP side, and a unique number is assigned to the lower 64 bits by the interface on the communication node side. In this way, when the communications are eavesdropped for a prescribed period of time by the malicious third person, it is not so difficult to identify that communication node.
In order to deal with demands for such a privacy protection, there is a proposition for randomly changing the lower 64 bits of the IPv6 address defined by RFC 3041 or the like.
In the case of using such a method for randomly changing the IP address, it is not customary to register RR (Resource Record) for the reverse look-up corresponding to this IP address (the reverse look-up is a procedure to obtain the host name from the IP address). This is because if the RR is registered into the name server of the DNS such that the host name can be obtained by the reverse look-up from a particular IP address, there is a problem that the IP address can be revealed at some specific timing from the host name even when the IP address is randomly changed, so that the privacy cannot be protected.
However, there are servers which regard the correspondent that attempted an access as a non-trustworthy communication node and do not permit an access from that communication node, when the reverse look-up or the normal look-up of the IP address from which the access is attempted is carried out and failed.
Also, there is a method for dynamically registering the host name that is automatically generated by using the dynamic update function of the DNS, but it is difficult to operate the DNS by accurately authenticating the dynamic update function.
Apart from these problems, there are servers which regard the correspondent that attempted an access as a non-trustworthy communication node and do not permit an access from that communication node, when the reverse look-up or the normal look-up of the IP address from which the access is attempted is carried out and failed. For this reason, the use of a random IP address as a default source address is not recommended in general.
Note that the details of the source address selection and the destination address selection under the IPv6 environment can be found in the IETF Internet draft “draft-ietf-ipngwg-default-addr-select-07.txt”.
As described, in the prior art, it has been impossible to protect the privacy of the communication node or the user sufficiently because of the leakage from the IP address. Also, in the method using a random IP address as a source address, the privacy protection can be realized but there are also problems such as that the connectivity cannot be guaranteed.